A standby electrical power generator or power supply functions in an electrical supply system as an alternative source of electrical power to substitute for the principal power generator or power supply, should the latter fail or be shut down. Requisite power continues to an electrical load, typically, an electronic or electrical apparatus that one wishes to continue to function, notwithstanding interruptions in the principal power generator or supply. The switch-over to the standby supply may be accomplished by devices as simple as an electromagnetic relay. The relay switches its relay contacts when the principal power supply fails and substitutes the back up power supply in the power distribution circuit, and, alternatively, switches back again when the principal power supply is restored. In general, many of those standby power supply techniques are known and may be found in industrial practice.
One particular application of power generators and power supplies and standby power supply systems is found within aircraft. Modern aircraft contain various electrical systems which consume, store, and/or generate electrical power; and electrical distribution systems for distributing the electrical power generated to the various electrical systems within the aircraft or, as variously termed, electrical loads. One such electrical load is the electrical motor that starts the aircraft's turbines; another is the radio; still another is the battery.
Much like the automobile, the aircraft contains a large battery, which stores charge which can be used to supply direct current ("DC") electricity and serves as a standby supply. When the pilot operates the start key, current from that battery enables electrical motors to start the aircraft's turbine. Once started, the engine continues operation through internal combustion of petrochemical fuels, and does not require continued energy depletion of the battery. Instead the engine spent electrical.
In addition to producing thrust, the aircraft's engines drive a turbine generator which in turn generates AC or DC power of a high voltage. That respective AC or DC power is distributed to a number of respective AC-to-DC or DC-to-DC converters which in turn supply electrical power at other voltages, either higher or lower voltages. A portion of the DC power being generated is typically used to replenish or recharge the main battery; that is, replenish the electrical energy drained from the battery in order to start the engines and to supply a steady "trickle charge current" to replace electrical energy that is gradually lost from the battery through the battery's internal leakage resistance. That trickle charge current procedure ensures that the battery remains at peak capacity to allow for subsequent engine starts.
When the aircraft is parked and its engines shut down, the turbine generators no longer generate electricity. The battery then serves as a standby power supply. All electrical systems should likewise be shut down, except for those few essential electronic devices that are intentionally designed to have continued access to the craft's main battery. As in the automobile, some electrical systems, such as an electric clock, remain connected to the main battery so that the systems may continue to operate even when the engine is not running.
Continued post engine shut down operation of those few essential electronic devices creates additional drain on the battery. Unless eventually recharged, the battery will eventually be drained of its stored electrical charge. Typically battery charging apparatus is on hand at the aircraft hangers for connection to the aircraft's distribution system. Operating from the land based electric utility system, as example, the portable battery charger serves the need to maintain the battery's charge, while the aircraft is parked over the long term. The foregoing aircraft electrical power supply system, supply back up and recharging apparatus would seem complete and covers every option to preclude unavailability of DC power.
Aircraft manufacturers are first concerned with having the aircraft remain airworthy for the safety of pilot and passenger. The power generation and distribution systems are designed and installed to meet that goal, and, as history attests, succeeded in that goal. While large airliners with access to service at major airports easily avoid dead batteries, smaller aircraft do not always operate under conditions in which they obtain the luxury of major airport service. They may operate in airports that are little more than a hanger and a runway, unequipped with sufficient battery chargers for available aircraft, and, sometimes, even without electricity.
The foregoing circumstance is particularly true for military aircraft. By design some military aircraft are intended to operate from clearings in the wilderness where no electricity is available. Unlike large commercial airliners, the design of aircraft for operation in such harsh environment requires a greater degree of self-sufficiency. The military aircraft cannot rely on support service always being available.
The foregoing briefly describes a few circumstances in which it is preferable to eliminate any drain on the aircraft's main battery and conserve that energy when the engines are shut down. A number of peripheral electronic avionics devices, not available from the aircraft manufacturer, are often installed in aircraft, particularly in military aircraft. Most of those electronic avionics devices are not intended for operation when the aircraft's engines are shut down. However, at least one such apparatus, the cryptographic messaging apparatus, should desirably continue in operation. Although such peripheral apparatus is given access to the aircraft's power distribution system for electric power when the engines are running, it is not desired to provide battery access for that apparatus when the engines are shut down.
One reason for a back up supply for such peripheral equipment is convenience. As example, the cryptographic electronic equipment requires the pilot to manually insert certain data into the apparatus, where that data is stored in random access memory. Should power to that apparatus be removed, the data in the memory is erased. The pilot is then required to repeat the laborious task of re-entering the data in order to use the cryptographic apparatus.
Those factors are not of concern to the aircraft manufacturer, who does not address them. To require the aircraft's entire electrical distribution system to comply with those requirements would raise the cost unnecessarily. The present inventors realize that the peripheral electronics apparatus should carry its own standby power source and rely on the main power source only when the aircraft's turbine engine is running.
Accordingly, an object of the present invention is to provide a standby power source within an aircraft's peripheral electronic communication equipment that is separate from any standby source for the aircraft's principal power system and dedicated to that communication equipment.
It is another object of the present invention to provide a standby power source for aircraft peripheral electronic equipment that is miniaturized and, more particularly, mechanically fits within a known SEME format.
It is a further object of the invention to ensure that an aircraft's peripheral electronic apparatus receives operating current continuously without even momentary interruption even in the event of failure or shutdown of the aircraft's turbine generator.
And it is a still further object of the invention to provide a standby power source to an electronic apparatus that normally receives electrical power over the main distribution line while maintaining practical electrical isolation between the standby power source and the main distribution line.